580ex power settings/ watts per second
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Old 02-17-2008   #1
Alpaca
 
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Default 580ex power settings/ watts per second

Does anybody know the conversion formula to equate the power settings on the 580ex (IE 1/16, 1/8, 1/4 etc.) to the equivalent watt seconds of energy the flash is putting out? Thanks in advance.

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Old 02-17-2008   #2
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Default Re: 580ex power settings/ watts per second

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Originally Posted by NUM2BIZ View Post
Does anybody know the conversion formula to equate the power settings on the 580ex (IE 1/16, 1/8, 1/4 etc.) to the equivalent watt seconds of energy the flash is putting out? Thanks in advance.
There is no conversion possible. First, watt seconds is the electrical power input to the flash capacitor... How much light comes out of the flash tube is another matter, depending on an efficiency factor. How much Guide Number is useful also mainly depends on the reflector and the angle of coverage, ie, the same power concentrated into a narrow beam is much brighter than a very wide floodlight effect.

Camera speedlights have focused reflectors providing many guide numbers, and the watt seconds concept is not used by them.

If you put two different flashes into the same umbrella and compare the metered output to other studio lights measured in watt seconds, you probably come up with a guess of around 75 to 80 watt seconds. That is, a 160 watt second AlienBees B400 will be a full stop stronger, double power.

The 1/16, 1/8, 1/4, 1/2 power levels each double the power of the previous smaller fraction. One f/stop per step.


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